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My Automotive FAQ - Synthetic oil vs. Toyota VVTL-i

Notice.  This information is from my first-hand experience with the engine in my 2000 Toyota Celica GT-S.  I encourage you to perform your own testing to determine the outcome for your engine.

The big question of late is whether or not the use if synthetic oil will alter (more specifically, negatively delay) the engagement of the high-RPM cams in the VVTL-i in the 2000 Celica GT-S.

Engine oil is for lubrication...   First of all, consider that the VVTL-i system uses engine oil as a hydraulic fluid, so there is the potential (not probability, not likelihood.. not cause for alarm, yet) that a synthetic oil may cause a change in the timing of the engagement.  Also consider that engine oil, both conventional and synthetic alike, is formulated primarily for lubrication, and secondarily for a host of other properties such as heat transfer, corrosion resistance, etc.   Up until Honda's VTEC and Toyota VVTL-i systems, engine oil had  not been used as a hydraulic fluid.  This is important to remember for the same reason that power steering systems and automatic trannys don't use engine oil.  Instead, these components use a fluid that is formulated as a hydraulic fluid.  

An oil's an oil's and oil, right?  Is that to say that you couldn't put engine oil (of a very light viscosity) in your power steering system?  You could, and it would likely get you out of a bind, but certainly this is not optimal for your PS system.  Or could you use auto tranny fluid (ATF) in your engine?  Certainly, but don't expect it to provide the same quality of lubrication as engine oil.  (Note: I'm not advocating the use of ATF in lieu of engine oil.  Rather, I'm stating that a quart of tranny fluid could be used in a pinch for a very short duration.  FWIW, ATF is extremely high detergent in nature and has been used prior to an oil change to flush the engine.)   Have you never wondered why there are (or at least were) two predominant types of ATF?   Type F and Dextron (nevermind the different flavors of Dextron).  Each was formulated slightly differently than the other.

NET-NET....  My point to this discussion is that even though (it's generally accepted that) synthetic oil provides superior lubricating qualities and resists hydrocarbon breakdown as compared to conventional engine oils, synthetic oil, regardless of viscosity, may impact the engagement of the high rpm cams in the VVTL-i system.  And don't assume that just because VTEC engines are not affected by this issue (I have no idea whether this is true or not, just merely making the case) that VVTL-i engines are also automatically immune.   

My testing...  After driving my car for nearly 15K miles, I feel pretty good about knowing how and when the high RPM cams engage on my car's engine.  So, I plan to switch back to conventional oil at the next oil change in order to conduct my own non-scientific test.  If possible, I'll time this oil change such that I can dyno the car with the conventional oil.  (I still need to validate the accretive power due to the RMM intake and exhaust.)  With dyno sheets of the engine on both synthetic and convention oil, I should be able to make a general conclusion as to whether synthetic oil has made any effect on the engine in my 2000 Celica GT-S.  I'll post the results on here when available.

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